E-Discovery Categories of Electronically Stored Information

In e-discovery, electronically stored information (ESI) is divided into five categories, which are grouped into two tiers based on the effort and cost needed to access ESI. Keep these categories in mind when requesting ESI or responding to a request:

ESI stored on removable media or accessed via automated or
robotic storage systems. Access speeds range from a few
milliseconds up to 2 minutes. Examples: optical disk
and magnetic tape.

First tier: reasonably accessible

Offline storage and archives

ESI sent to storage. Unlike the first two categories, offline
ESI is accessed manually. Examples: magnetic tape or
optical disks; referred to as JBOD (just a bunch of
disks).

First tier: reasonably accessible

Backup tapes, commonly using data compression

ESI stored for backup or disaster recovery and not organized
for retrieval of specific files or messages. Retrieving ESI
requires restoring the entire tape and might require reversing the
compression used to fit more bytes of data. The discovery of ESI
from backup tapes requires proof that their need and relevance
outweigh their retrieval and processing costs.
Example: backup tapes.

Second tier: not reasonably accessible

Erased, fragmented, or corrupted data

Erased, overwritten, fragmented (broken up and stored in
separate areas), or corrupted files (damaged by computer viruses,
or a hardware/software malfunction) are the least accessible. This
ESI might be accessed only after significant processing or might be
impossible to access at all.